The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Engineered limb prosthetics hold great potential for millions of spinal cord injury, neuromuscular disease, and amputation victims. Although sophisticated microelectronics and robotics facilitate ever closer approximations of human movement, interfacing the mechanical to the biological has proved challenging. Furthermore, providing graded sensory feedback from the prosthetic to the individual is critically important. Fundamentally, interface technologies must transduce neuron-based bioelectric action potentials saltatory conduction along myelinated axons mediated by mass transfer (ion currents) directly or indirectly to an electrical current through a metallic conductor. Multiple studies have dramatically demonstrated volitional prosthetic control using implanted cortical electrodes in primate models. With these successful demonstrations, the practical aspects of using central neural electrodes for human deployment including their surgical invasiveness, biofouling, encapsulation, foreign body response, and reliance on capacitive and high impedance electronics—all which lead to time-related signal degradation—become foremost challenges.
To avoid some of these obstacles, natural functional and anatomic separation of axons into fascicles in the peripheral nervous system may provide a more attractive interface site. Indeed, neurotization, or targeted muscle reinnervation procedures exploit peripheral nerve sorting, biologic plasticity, and ultimately, neuromuscular junction stability. Expanding this concept to human volitional prosthetic control, some in the field have recently demonstrated that Targeted Muscle Reinnervation (TMR), or independent reinnervation of several individual muscle partitions by isolated nerves (from the brachial plexus), could indirectly drive a robotic prosthetic through surface EMG (electromyography) recordings. These exciting clinical results are already being deployed in select patients, but donor muscle limitations and reliance on non-integrated surface EMG may preclude achieving individual axonal fidelity (i.e. proximal interphalangeal joint flexion of the index finger), and sensory feedback has only been partially addressed.